1. Field of the Invention
This invention relates to a measuring instrument, more particularly to a measuring instrument adapted to measure a chain.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a chain 100 adapted to be mounted on a bicycle (not shown) comprises a plurality of spaced apart meshing spaces 101, a plurality of outer chain plates 103, a plurality of inner chain plates 104 each abutting against two adjacent ones of the outer chain plates 103, and a plurality of chain rollers 102 each extending through two of the outer chain plates 103 and two of the inner chain plates 104. The chain rollers 102 tend to wear out due to engagement of teeth of a sprocket (not shown) with the meshing spaces 101. Wearing of the chain rollers 102 results in an increase in total length of the chain 100 during use of the bicycle. Hence, the sprocket teeth cannot mesh with the meshing spaces 102 in a tight fitting manner, thereby affecting adversely smooth transmission of force.
A conventional measuring instrument 11 is adapted to measure such change in the total length of the chain 100. The measuring instrument 11 has spaced apart first and second measuring portions 111, 112. The distance between the first and second measuring portions 111, 112 is fixed and is equal to an allowed maximum distance between two selected ones of the meshing spaces 101 of the chain 100 when the chain 100 is stretched to a maximum allowable extent.
When it is desired to measure the chain 100, the first measuring portion 111 is first inserted into a first selected one of the meshing spaces 101 of the chain 100. Afterwards, the second measuring portion 112 is tried to be inserted into a second selected one of the meshing spaces 101 of the chain 100. If the second measuring portion 112 can be inserted fully into the second selected meshing hole 101, a user can realize that the chain 100 is excessively long. However, the user cannot realize the difference between actual total length and standard total length of the chain 100 from the measurement of the conventional measuring instrument 11.